1. Field of the Invention
The present invention relates generally to a temperature control apparatus and method, and a program. In particular, the invention relates to a temperature control apparatus and method that use a Peltier device to efficiently control the temperature of a control target that needs both cooling and heating applications and to a program therefor.
2. Description of the Related Art
In recent years the Peltier device has been used to control the temperature of a control target as cooling application (see e.g. Japanese Patent Laid-open No. 2005-250249).
For example, FIG. 1 illustrates the configuration of an existing temperature control system (hereinafter, referred to as the existing system) using a Peltier device by way of example.
The existing system of FIG. 1 is configured to include a control target 11 through a cooling fan 16.
The existing system of FIG. 1 is provided with a Peltier system 12 in order to cool the control target 11.
The Peltier device 12 is a device having the Peltier effect. The Peltier effect is a phenomenon in which when electric current flows through the junction between dissimilar conductors, e.g., p-type and n-type conductors, heat absorption occurs at the junction. The Peltier device is configured such that a plurality of p-type and n-type semiconductors are alternately joined on the respective opposed sides of a pair of substrates through a conductor. When the Peltier device is energized, one of the substrate sides becomes a heat-absorbing side and the other becomes a heat-generating side.
In the example of FIG. 1, the A-side of the Peltier device 12 is used as a heat-absorbing side and the B-side is used as a heat-generating side. In addition, a control target is disposed close to the A-side. When a predetermined positive voltage value is applied to the Peltier device 12, a temperature difference ΔT corresponding to the positive voltage value occurs between the A-side and the B-side. Here, since the A-side becomes the heat-absorbing side, the temperature difference ΔT occurs in which the B-side has high temperatures and the A-side has low temperatures. Thus, the heat radiated by the control target 11 is absorbed by the A-side, with the result that the control target can be cooled.
For example, a controller 15 composed of e.g. dedicated hardware, a computer, etc. determines a predetermined positive voltage value as a command voltage to the Peltier device 12 on the basis of the temperature sensed by a temperature sensor 14 which measures the temperature of the control target 11. The controller 15 changes the temperature difference ΔT of the Peltier device 12 by applying the command voltage to the Peltier device 12, consequently exercising the temperature control so as to cool the control target 11. Incidentally, the command voltage mentioned above refers to a drive voltage for the Peltier device 12.
In this temperature control, as the sensed temperature of the control target 11 is higher than the control target value, that is, as an error (temperature difference) between the sensed temperature and the control target value is increased, the command voltage, namely, the positive voltage value from the controller 15 is increased. Thus, the temperature difference ΔT of the Peltier device 12 is increased accordingly.
In the Peltier device 12 in this case, if the temperature of the B-side is constant, the temperature of the A-side drops according to the increase of the temperature difference ΔT, which enhances the cooling effect of the control target 11. Then, the sensed temperature of the control target 11 gradually drops to come close to the control target value. In other words, the error (temperature difference) between the sensed temperature and the control target value gradually decreases. In addition, the command voltage, i.e., the positive voltage value from the controller 15 gradually decreases. Also the temperature difference ΔT of the Peltier device 12 gradually decreases accordingly. Finally, the sensed temperature of the control target 11 coincides with the control target value, that is, the error (temperature difference) between the sensed temperature and the control target value is eliminated. Thus, the command voltage from the controller 15 becomes zero and also the temperature difference ΔT of the Peltier device 12 is eliminated.
However, in the Peltier device 12 in FIG. 1, the B-side functions as a heat-generating side to causes a heating phenomenon, which is a phenomenon reverse to the cooling phenomenon of the A-side. The temperature of the B-side rises unless some kinds of measures are applied to the B-side. In this case, if the command voltage from the controller 15 is constant, that is, if the temperature difference ΔT of the Peltier device 12 is constant, the temperature of the A-side rises as a result of the increased temperature of the B-side, which reduces the cooling effect of the control target 11. According to circumstances, also the sensed temperature of the control target 11 rises to a level higher than the control target value. In other words, the error (temperature difference) between the sensed temperature and the control target value increases. Also the command voltage from the controller 15, i.e., the positive voltage value rises accordingly. That is to say, unless the increased temperature of the B-side is suppressed, the temperature difference ΔT of the Peltier device is further increased. Finally, at the stage where the temperature difference ΔT excesses a permissible value, the Peltier device 12 goes out of control (becomes uncontrollable).
Accordingly, it is necessary to suppress the increased temperature of the B-side in order to enhance the cooling effect on the control target 11 and to prevent the Peltier device 12 from going out of control. To meet the necessity, the existing system of FIG. 1 includes a radiator 13 to radiate heat from the B-side and the cooling fan 16 to cool the radiator 13. Incidentally, Japanese Patent Laid-Open No. 2005-250249 employs a heat sink as the radiator 13.